The invention relates generally to the field of electrical powered steering wheel systems and in particular to a system and method for sensing angular rotation position and torque.
Electrically powered steering wheel systems have been developed to meet the tighter fuel economy standard. This is achieved by replacing a belt-driven hydraulic pump, which is constantly running whether assistance is required or not, with a brushless DC motor (BLDC). The electric motor is activated only when the steering assist is required, thereby saving energy. Another major advantage is the elimination of a belt-driven engine accessory, and several high-pressure hydraulic hoses between the hydraulic pump, mounted on the engine, and the steering gear, mounted on the chassis. This greatly simplifies manufacturing and maintenance. By incorporating electronic stability control, electric power steering systems can instantly vary torque assist levels to aid the driver in corrective maneuvers. As a result, there is a rapid increase in the demand for steering wheel sensing systems which are low cost and reliable.
FIG. 1 illustrates a high level block diagram of an electrical powered steering wheel system 10 known to the prior art, electrical powered steering wheel system 10 comprising: a steering wheel 20; a steering angular position sensor 30; a torque sensor 40; a vehicle speed sensor 50; an electronics control unit (ECU) 60; a motor 70, in one embodiment comprising a BLDC motor; a reduction gear 80; and a steering column 90. Steering angular position sensor 30 is arranged to track the rotation of steering wheel 20 and ECU 60 is arranged to determine the angular position of steering wheel 20 responsive to the tracking of steering angular position sensor 30. ECU 60 is further arranged, in cooperation with torque sensor 40, to determine the torque applied to steering wheel 20. Responsive to the determined angular position and applied torque, ECU 60 is arranged to apply assistive torque via motor 70 to reduction gear 80 or steering column 90. The applied assistive torque is further responsive to the speed of the vehicle detected by vehicle speed sensor 50.
As illustrated, system 10 relies primarily on steering angular position sensor 30 and torque sensor 40. U.S. Pat. No. 7,726,208, granted Jun. 1, 2010 to Hoeller et al., the entire contents of which incorporated herein by reference, is addressed to a combined steering and torque sensor. Unfortunately, the design of Hoeller requires several sensor circuits, which thus requires separate integrated circuits for the steering angle sensor element and the steering torque sensor element, which adds to cost.